1. Field of the Invention
The present invention relates to a novel dielectric material composition with high dielectric constant and low dielectric loss, which comprises a metal oxide having a pervoskite structure with a general formula Ba1-xM1xTi1-yM2yOm.
2. Description of the Related Art
Thin-film ferroelectric materials have applications in various electronic devices, such as dynamic and ferroelectric random access memories (“DRAM” and “FRAM”). Thin-film ferroelectric materials are also widely used in the development of new microwave devices such as frequency agile filters, phase shifters, and tunable high-Q resonators. Integrated circuit devices are currently developed toward higher and higher integration densities as well as high frequencies. Therefore, it is important for these devices to have a substantially high capacitance per unit area and, at the same time, possess a high Q factor and modulation capability during operation at high frequencies. Most attention has been focused on Ba1-xSrxTiO3 (BST) for this type of application material, as these materials possess high dielectric constants and low loss (that is, high Q factor). BST is a ferroelectric with the pervoskite structure. By the incorporation of SrTiO3, the Curie point of BaTiO3 at 130° C. can be shifted to around room temperature for Ba0.7Sr0.3TiO3, thus achieving the maximum dielectric constant around the operating temperature. At room temperature, single crystal SrTiO3 has a very low loss (tan δ<10−4) but also a low dielectric constant. On the other hand, BaTiO3 has a very high dielectric constant but a high loss. Mixing Sr and Ba has resulted in BST materials with high dielectric constants and improved tan δ over BaTiO3. Most investigations are focused on memory devices where measured frequencies range from 1 to several MHz with little discussion on the GHz level. According to the literature, the bulk material of the composition of Ba1-xSrxTiO3 has a dielectric constant, ∈r, of 300, 760, 990, and 230, and a dielectric loss, tan δ, of 0.5, 0.02, 0.04, and 0.02, measured at 20° C. and a frequency of 1 GHz when x is 0, 0.44, 0.38, and 1, respectively. The dielectric loss still has room for improvement. In view of the potential for more stringent requirements for materials in the future due to the operation of the devices at a frequency of several GHz and at a raised temperature resulting from device integration, the improvement of electric and frequency properties for BST is needed.
The important properties of dielectric materials, for example, dielectric constant and dielectric loss, often vary as temperature or frequency varies. Thus the operation range for application varies accordingly. Furthermore, the improvement of one property (such as, dielectric constant) always causes other properties (such as, dielectric loss) to deteriorate.
U.S. Pat. No. 6,146,907 discloses a dielectric thin film having a general formula, (BaxSryCa1-x-y)TiO3. U.S. Pat. No. 6,277,436 discloses a dielectric material, comprising a metal titanate film composed of at least 60 atom % titanium, (Zr,Sn)TiO4, Zr1-xSnxTiO4, and the oxide of (BaxSryTi1-x-y). The metal oxides mentioned above are different from Ba1-xM1xTi1-yM2yOm of the present invention.